Microcircuit packages such as plug-in packages and flat packs have been used for many years to hermetically protect hybrid and semiconductor discrete and integrated circuit chips. The chip or chips are bottom-mounted within a metal frame, i.e., eyelet or body, of the package and electrically connected to external circuitry by means of conductive leads or pins passing through apertures in the bottom or frame. To ensure hermetic sealing and to preclude short circuiting between the leads and the metal package, the leads are sealed in insulative preforms and the insulative preform-lead combinations are sealed in the apertures of the bottom or frame.
Thus, each lead of prior art packages provided only a single conductive pathway between the integrated circuit chip mounted within the package and external circuitry. In general, the sizing of the package is dictated by the size of the ICs mounted therein. As the chip size decreases, the size of the package is decreased accordingly. Smaller package sizes, however, are generally limited as to the number of apertures that may be formed through the frame thereof, and concomitantly, the number of leads associated therewith. Forming more apertures in the frame of the metal package tends to weaken the overall structural integrity thereof since the spacing between apertures is decreased. For hermetically sealed metal packages and/or metal packages disposed in overpressurized or vacuumized environments, any decrease in the structural integrity of the metal package may lead to decreased package reliability in the operating environment.
The trend in the electronic industry is towards the utilization of very large scale integrated (VLSI) and microwave/millimeter-wave monolithic integrated circuit (MMIC) technology since such technology provides increased operational performance with smaller sized ICs. These technologies, however, require increased conductive pathway densities to accommodate increased data handling capabilities.
For many applications, such as avionics and space applications, the VLSI and MMIC components must be packaged within hermetically sealed packages. The configuration of prior art packages are generally incompatible with VLSI and MMIC technology due to the increased conductive pathway densities required. Increasing the number of conductive leads in prior art packages requires a concomitant increase in the number of apertures formed in the frame of the metal package, which generally requires an increase in overall package size and weight. The number of holes which may be formed in the body, however, is generally constrained by size, weight and structural considerations as discussed hereinabove.
One solution to the above-described problem is to utilize smaller diameter conductive leads which would permit a limited increase in conductive pathway density. Smaller conductive leads, however, are more fragile and subject to catastrophic failure during fabrication, handling, installation and/or operation in dynamic environments that are typically encountered in aerospace operations. In addition, smaller conductive leads require smaller apertures, and smaller apertures are more difficult to produce with consistent results. Moreover, smaller leads and smaller apertures require smaller insulative preforms to form the glass-to-metal seals. These smaller elements are difficult to handle and fabricate, thereby increasing the overall cost of the finished package.